I´m asking how to connect two or more tables from an MS Access table into c# Windows forms?.
I get the error, that ue cant find the second table:
public partial class Form1 : Form
{
private OleDbConnection connection = new OleDbConnection();
private OleDbConnection connection2 = new OleDbConnection();
public Form1()
{
connection.ConnectionString = #"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\be\Documents\MitarbeiterDaten2.accdb;
Persist Security Info=False;";
connection2.ConnectionString = #"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\be\Documents\DatenbankAbteilung.accdb;
Persist Security Info=False;";
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
try
{
connection.Open();
OleDbCommand command = new OleDbCommand();
command.Connection = connection;
string query = "select ABTEILUNG from combo";
command.CommandText = query;
OleDbDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Abteilung.Items.Add(reader["ABTEILUNG"].ToString());
}
connection.Close();
}
catch (Exception ex)
{
MessageBox.Show("Error" + ex);
}
finally
{
connection.Close();
}
Anybody got an solution?
Its just about, how to connect two or more MS Access tables into C# Windows forms.
You can reuse the the objects, and can get data from various tables or databases, as :
private void Form1_Load(object sender, EventArgs e)
{
try
{
connection.Open();
OleDbCommand command = new OleDbCommand();
command.Connection = connection;
string query = "select ABTEILUNG from combo";
command.CommandText = query;
OleDbDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Abteilung.Items.Add(reader("ABTEILUNG").ToString());
}
reader.Close(); //' Always Close ther Reader. Don't left it open
connection2.Open();
command.Connection = connection2; //' Reusing Same Command Over New Connection
command.CommandText = "Select Field2 from Table2";
while (reader.Read)
{
if (!(Convert.IsDBNull(reader("Field2")))) //' Checking If Null Value is there
{
Abteilung.Items.Add(reader("Field2").ToString());
}
}
reader.Close();
}
catch (Exception ex)
{
MessageBox.Show("Error" + ex);
}
finally
{
connection.Close();
connection2.Close();
}
}
How about using using blocks to take care of the commands and connections and then using DataAdapter to get the job done easily. I use some code like this.
DataSet ds = new DataSet();
using (OleDbConnection con = new OleDbConnection(MDBConnection.ConnectionString))
{
con.Open();
using (OleDbCommand cmd = new OleDbCommand("SELECT Column FROM Table1", con))
{
using (OleDbDataAdapter da = new OleDbDataAdapter(cmd))
{
da.Fill(ds);
}
}
using (OleDbCommand cmd = new OleDbCommand("SELECT AnotherColumn FROM Table2", con))
{
using (OleDbDataAdapter da = new OleDbDataAdapter(cmd))
{
da.Fill(ds);
}
}
}
return ds;
Related
namespace PCMS
{
public partial class frmPlayerInterface : Form
{
private OleDbConnection con = new OleDbConnection();
OleDbCommand com = new OleDbCommand();
private DataTable dt = new DataTable();
public frmPlayerInterface(string getUser)
{
InitializeComponent();
con.ConnectionString = #"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\Projects\SDP\PCMS\SDP.accdb";
lblUser.Text = getUser;
}
private void btnEnquire_Click(object sender, EventArgs e)
{
frmEnquire frmenq = new frmEnquire();
frmenq.ShowDialog();
}
private void btnTopUp1_Click(object sender, EventArgs e)
{
frmTopUp frmTU = new frmTopUp();
frmTU.ShowDialog();
}
private void frmPlayerInterface_Load(object sender, EventArgs e)
{
con.Open();
OleDbCommand comm = new OleDbCommand();
String sql = "select Balance from PlayerAccount where Player_User=#user";
comm.Parameters.Add(new OleDbParameter("user", lblUser.Text));
comm.CommandText = sql;
OleDbDataReader cursor = comm.ExecuteReader();
while (cursor.Read())
{
lblBalance.Text = cursor["Balance"].ToString();
}
con.Close();
}
}
}
Hey sorry guys asking this again but ive been trying this for the past three hours and wave the white flag. Still getting the same error.
I just want to have the selected balance value from the database to be shown in the label.
Thanks ><
You're not associating the connection with the command object:
con.Open();
String sql = "select Balance from PlayerAccount where Player_User=#user";
OleDbCommand comm = new OleDbCommand(sql, con);
Note that reusing a connection is not always the best design. Connections are pooled in .NET, so recreating them is generally not an expensive operation. A better design would be to store the connection string as a class property then just create a connection when you need it:
private string ConnectionString = #"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\Projects\SDP\PCMS\SDP.accdb";
// or better yet - pull form app.config...
and when you use it:
String sql = "select Balance from PlayerAccount where Player_User=#user";
using(OleDbConnection con = new OleDbConnection(ConnectionString))
{
con.Open();
using(OleDbCommand comm = new OleDbCommand(sql, con))
{
... Add parameters, execute query, return results
}
}
I am using the below code to access the MS Access Database. But i got a error message Fill: SelectCommand.Connection property has not been initialized.How can i solve this issue.
common.cs
=========
public static bool DBConnectionStatus()
{
try
{
string conString = #"Provider=Microsoft.Jet.OLEDB.4.0; Data Source=|DataDirectory|db_admin.mdb; Jet OLEDB:Database Password=admin";
using (OleDbConnection conn = new OleDbConnection(conString))
{
conn.Open();
return (conn.State == ConnectionState.Open);
}
}
catch (OleDbException)
{
return false;
}
protected void btn_general_Click(object sender, EventArgs e)
{
try
{
bool state = common.DBConnectionStatus();
if (state == true)
{
cmd = new OleDbCommand("select * from tbl_admin");
da = new OleDbDataAdapter(cmd);
DataSet ds = new DataSet();
da.Fill(ds); // Error Here
if (ds.Tables[0].Rows.Count > 0)
{
}
}
}
catch (Exception e1)
{
}
}
I did suggest you to modify your code to something like this:
private DataTable YourData()
{
string conString = #"Provider=Microsoft.Jet.OLEDB.4.0; Data Source=|DataDirectory|db_admin.mdb; Jet OLEDB:Database Password=admin";
DataSet ds = new DataSet();
using (SqlConnection conn = new SqlConnection(conString))
{
try
{
conn.Open();
SqlCommand command = new SqlCommand("select * from tbl_admin", conn);
command.CommandType = CommandType.Text;
SqlDataAdapter adapter = new SqlDataAdapter(command);
adapter.Fill(ds);
if (ds.Tables[0].Rows.Count > 0)
{
// do somethign here
}
}
catch (Exception)
{
/*Handle error*/
}
}
return ds.Tables[0];
}
And then:
protected void btn_general_Click(object sender, EventArgs e)
{
this.YourData(); // you will get the Data here. you can then use it the way you want it
}
You are initializing a Command which you use to construct a DataAdapter, but both without setting the required Connection property:
cmd = new OleDbCommand("select * from tbl_admin"); // <-- no connectuion assigned
da = new OleDbDataAdapter(cmd); // <-- no connectuion assigned
So your exception is pretty self-explanatory.
One final note: using will dispose/close the connection, so the method DBConnectionStatus is pointless. So don't use it, instead use the using in in the first place:
try
{
using(var con = new OleDbConnection(connectionString))
using(var da = new OleDbDataAdapter("elect * from tbl_admin", con))
{
var table = new DataTable();
da.Fill(table); // note that you don't need to open the connection with DataAdapter.Fill
if (table.Rows.Count > 0)
{
// ...
}
}
}
catch (Exception e1)
{
// don't catch an exception if you don't handle it in a useful way(at least loggging)
throw;
}
As per your requirement you can also use SqlDataAdapter instand of ExecuteReader.
public void ReadMyData(string connectionString)
{
string queryString = "SELECT OrderID, CustomerID FROM Orders";
using (OleDbConnection connection = new OleDbConnection(connectionString))
{
OleDbCommand command = new OleDbCommand(queryString, connection);
connection.Open();
OleDbDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Console.WriteLine(reader.GetInt32(0) + ", " + reader.GetString(1));
}
// always call Close when done reading.
reader.Close();
}
}
I have written some C# to update a MySql table but I get an exception every time I call the method ExecuteNonQuery(). I have researched this on the web and every solution I find produces the same error. I have an open connection to the database and the update query to the database is written correctly. The code that I have so far come up with is :
public int executeUpdate()
{
int result = 0;
if (isConnected)
{
try
{
MySqlConnection cn = new MySqlConnection(connection.ConnectionString);
MySqlCommand cmd = new MySqlCommand();
cmd.Connection = cn;
cmd.CommandText = "UPDATE test SET status_id = 1 WHERE test_id = 1";
int numRowsUpdated = cmd.ExecuteNonQuery();
}
catch (MySqlException exSql)
{
Console.Error.WriteLine("Error - SafeMySql: SQL Exception: " + query);
Console.Error.WriteLine(exSql.StackTrace);
}
catch (Exception ex)
{
Console.Error.WriteLine("Error - SafeMySql: Exception: " + query);
Console.Error.WriteLine(ex.StackTrace);
}
}
else
Console.Error.WriteLine("Error - SafeMySql: executeQuery failed. Not connected to DB");
}
Change your try section to the code below:
try
{
using(MySqlConnection cn = new MySqlConnection(connection.ConnectionString))
{
MySqlCommand cmd = new MySqlCommand();
cmd.Connection = cn;
cmd.CommandText = "UPDATE test SET status_id = 1 WHERE test_id = 1";
cn.Open();
int numRowsUpdated = cmd.ExecuteNonQuery();
cmd.Dispose();
}
}
The connection must be opened before you execute a command. In the example above the command object will immediately be disposed and the connection object will implcitly be closed and disposed when you leave the using section.
I don't see the connection being opened.
Here is an example from MSDN: even inside a using block, they open the connection explicitly
private static void CreateCommand(string queryString,
string connectionString)
{
using (SqlConnection connection = new SqlConnection(
connectionString))
{
SqlCommand command = new SqlCommand(queryString, connection);
command.Connection.Open();
command.ExecuteNonQuery();
}
}
Edit: The principle is the same for MySQL as it is for SQL Server:
public void CreateMySqlCommand(string myExecuteQuery, MySqlConnection myConnection)
{
MySqlCommand myCommand = new MySqlCommand(myExecuteQuery, myConnection);
myCommand.Connection.Open();
myCommand.ExecuteNonQuery();
myConnection.Close();
}
I know how to connect, open, read, close as you see below. I also have awesome tutorial how to add update/delete etc.
I can connect dataTable to sql using asp.net controls, but I want to learn how to manipulate it from C#.
MasterCust is my gridview table name. How do I connect the to it?
protected void Page_Load(object sender, EventArgs e)
{
SqlConnection Conn = new SqlConnection("Data Source=aserver;Initial Catalog=KennyCust;Persist Security Info=True;user id=sa;pwd=qwerty01");
SqlDataReader rdr = null;
string commandString = "SELECT * FROM MainDB";
try
{
Conn.Open();
SqlCommand Cmd = new SqlCommand(commandString, Conn);
rdr = Cmd.ExecuteReader();
while (rdr.Read())
{
Console.WriteLine(rdr[0]);
}
}
finally
{
if (rdr != null)
{
rdr.Close();
}
if (Conn != null)
{
Conn.Close();
}
}
//MasterCust.
//MasterCust.DataSource = commandString;
//MasterCust.DataBind();
}
Edit: This code worked
try
{
Conn.Open();
SqlCommand Cmd = new SqlCommand(commandString, Conn);
SqlDataAdapter sdp = new SqlDataAdapter(Cmd);
DataSet ds = new DataSet();
sdp.Fill(ds);
//rdr = Cmd.ExecuteReader();
MasterCust.DataSource = ds.Tables[0];
MasterCust.DataBind();
}
Set the GridView's Datasource property and simply call the DataBind method.
This code will work. ( Tested)
SqlConnection Conn = new SqlConnection("Data Source=Localhost\\SQLEXPRESS;Initial Catalog=Flash2;Integrated Security=True;");
SqlDataReader rdr = null;
string commandString = "SELECT * FROM USER_MASTER";
try
{
Conn.Open();
SqlCommand Cmd = new SqlCommand(commandString, Conn);
rdr = Cmd.ExecuteReader();
MasterCustView.DataSource = rdr;
MasterCustView.DataBind();
}
catch (Exception ex)
{
// Log error
}
finally
{
if (rdr != null)
{
rdr.Close();
}
if (Conn != null)
{
Conn.Close();
}
}
I have a SQL Server Compact Edition Database file, and I want to display all the tables on it as nodes into a TreeView control in my windows application.
Unfortunately, I don't know how to.
This is what I have now:
private void PopulateTreeView()
{
SqlCeCommand cmd = new SqlCeCommand();
try
{
using (SqlCeConnection conn = new SqlCeConnection("Data Source=" + connString))
{
cmd.CommandType = CommandType.Text;
cmd.CommandText = "SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES";
conn.Open();
cmd.Connection = conn;
cmd.ExecuteNonQuery();
// Don't know what's next...
}
}
catch (Exception x)
{
MessageBox.Show(x.GetBaseException().ToString(), "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
finally
{
cmd.Dispose();
}
}
something like
var tv = new TreeView();
using(var conn = new SqlCeConnection("Data Source=" + connString))
using(var cmd = new SqlCeCommand(conn,"SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES"))
{
conn.Open();
if(conn.State != ConnectionStatus.Open) return;
cmd.CommandType=CommandType.Text;
using(var rdr = cmd.ExecuteReader())
{
while(rdr.Read())
{
tv.Nodes.Add(new TreeNode(rdr.GetString(0));
}
}
}
you can get fancier with the node creation. Have a look at the various constructors to see what you want.